Method for the storage of a liquefied gas in the presence of an adsorbant support having open cells

ABSTRACT

A process of storing a liquefied gas for distribution exclusively in gaseous form in an atmosphere whose pressure is less than that of the storage pressure, comprising disposing in a storage chamber conjointly with a stored liquefied gas, a minimum quantity of a capillary adsorbant support having open cells, the mean diameter of the cells being equal at most to 500 microns and the mean thickness of the intercellular walls being at most equal to 50 microns. The actual volume of the adsorbant support constituted by the volume remaining after deduction of all interstitial spaces of the minimum quantity, being: 
     A. at least 2% of the volume of the storage chamber for a capillary support having open cells, the mean volume of each, once in place, being equal to that of a sphere of a diameter of 40 microns with a mean thickness of the intercellular wall of about 4 microns and varying between 2 and 8 microns, 
     B. at least 12% of the storage chamber for a capillary support having open cells in which the mean volume of each cell corresponds, once in place, to that of a sphere of a diameter of 200 microns with a mean wall thickness of 30 microns and varying between 20 and 60 microns.

FIELD OF THE INVENTION

The invention relates to improvements in the storage of liquefied gas, for supply exclusively in gaseous form, in cigarette lighters, heating or lighting apparatus, or other such arrangements.

In the present description, the expression "liquefied gas" includes all gases whose critical temperature is greater than the ambient temperature; the expression "apparatus having an exclusively gaseous discharge" or the like refers to an apparatus having a liquefied gas storage in which the gas is released exclusively in the gaseous phase at the time of first use of the apparatus and up to its complete emptying; and the expression "adsorbant support" includes all capillary products having open cells.

PRIOR ART

It has already been proposed in French Pat. No. 897,877 to provide for storage of a gas in a storage chamber by means of a suitably chosen adsorbant support to return the gas to a pressure in the neighborhood of the pressure of utilization. The patentee thus contemplated an apparatus for exclusive gaseous discharge whose operation would be assured, following the teaching in the patent, of a "simple conduit of very small section advantageously combined with a spigot, or a flap or an obstruction valve."

The proposed adsorbant supports were cotton, peat, infusorial earth, silicates, metallic foams, higher homologues of hydrocarbons, in the case of the storage of hydrocarbons, cellulosic material and their derivatives, metallic salts, etc. when the cited gas comprises carbon dioxide, ammonia, oxygen, volatile perfume spirits, butane or analagous products and hydrogen sulfide.

In reality, the construction was never commercialized, either before or after its patenting for apparatus containing a liquefied gas in the presence of an adsorbant support whose discharge was exclusively gaseous and which operated uniquely due to a conduit of very small section. In fact, all apparatus having a system of gas distribution by a conduit of a very small section comprise a metallic mass such that the liquid to be evaporated always receives the necessary heat for its evaporation in spite of the cooling provoked by the evaporation.

In practice, this has never been realized, to the knowledge of the Applicant, in apparatus for purely gaseous discharge utilizing liquefied gas housed in an adsorbant support with the exclusion of any auxiliary apparatus.

It is to be further noted, that in the course of testing by Applicant of the storage of the liquefied butane or pentane in contact with cotton, felt, or charcoal, it has been found, on the one hand, that whatever the nature of the adsorbant, the pressure at the interior of the storage receiver is substantially the same as if the liquid had been stored without the adsorbant support, and on the other hand contrary to what seems to be stated in the previous patents, a partial condensation is always produced at the outlet of the reservoir such that fine droplets are present in the discharged gaseous phase.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a method for storing a liquefied gas in an apparatus for discharge exclusively in the gaseous phase utilizing only an adsorbant support.

Another object of the present invention is to provide a method of storing a liquefied gas which permits obtaining an exclusively gaseous discharge and at a substantially constant pressure at the outlet of the storage reservoir without utilizing an auxiliary expansion member.

The process is essentially characterized by the fact that there is disposed in the storage chamber conjointly with the liquefied stored gas, a minimum quantity of a capillary adsorbant support having open cells, the mean diameter of the cells being equal at most to 500 microns and the mean thickness of the intercellular wall being at most equal to 50 microns, the actual volume i.e. the volume remaining after deduction of all the interstitial spaces, of said minimum quantity, occupying:

a. at least 2% of the volume of the storage chamber in the case of a capillary support having open cells whose mean volume of each cell corresponds once in place, to that of a sphere of a diameter of 40 microns with a mean thickness of the intercellular wall of about 4 microns and varying between 2 and 8 microns;

b. at least 12% of the storage chamber in the case of a capillary support having open cells in which the mean volumes of each cell corresponds, once in place, to that of a sphere of a diameter of 200 microns, with a mean wall thickness of 30 microns and varying from 20 to 60 microns.

To determine the minimum quantity of the actual volume of the adsorbant support, the storage chamber has been filled in an amount of 40% which corresponds to a storage of 12.8 cm³ of liquid butane in a chamber of total volume of 32 cm³. This criteria may appear to be arbitrary but it permits definition with precision of the domain covered by the process of the invention.

Furthermore, the invention is also concerned with apparatus for effecting the process.

It follows from the preceding that the process of storage according to the invention presents a difference in principle from the known processes.

In fact, if a porous material could be compressed in such manner that it no longer had any free space at the interior of the cells, nor between the walls of the storage chamber and the adsorbant support, it would not be practically possible to make it adsorb a liquid. This is why, up to the present, it has been sought in known apparatus having a liquefied gas whose storage chamber is filled with an adsorbant support to compress the adsorbant support as little as possible in order to leave the maximum free space in which the liquefied gas can be stored.

In contrast, the Applicant contemplates not to store the maximum quantity of liquefied gas in a given chamber, but to obtain an apparatus having an exclusively gaseous discharge. To this end, it is necessary to augment to a certain degree the quantity of adsorbant support in a given chamber, which is equivalent to compressing the adsorbant support in said chamber.

However, contrary to what one might assume, from the fact that this compression necessarily leads to a diminution of the free space in which it is possible to store the liquefied gas, it has been found from tests that the degree of possible fill for an apparatus with exclusive gaseous discharge increases up to a certain value when the utilized adsorbant support is compressed.

It is in this province that the assembled results in one of the annexed drawings will be studied hereafter.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a graph referring to about one hundred tests of the storage of butane with diverse adsorbant supports; and,

FIG. 2 is a photograph enlarged 100 times, of a polyurethane foam utilized in one of the tests to be described hereafter.

DETAILED DESCRIPTION

In FIG. 1, the curves represented refer to the following compositions:

Curve 1: polyurethane foam having open cells from 200 to 500 microns in diameter, before compression, the mean thickness of the intercellular walls being of the order of 8 microns (FIG. 2):

Curve 2: polyisoprene foam having open cells from 300 to 500 microns in diameter, before compression, the mean thickness of the intercellular walls being of the order of 12 microns.

The butane utilized for the tests was butane of commercial quality whose exact composition in % by weight is as follows:

    ______________________________________                                         n - butane           78%                                                       isobutane            20%                                                       propane             1.5%                                                       butene, isobutane,                                                             pentanes            0.5%                                                       ______________________________________                                    

All the tests were effected in a test tube of 32 cm³ at a temperature of 20° C and the process of each test was the following:

place in the test tube a certain quantity of support;

weigh the test tube to determine the weight of the adsorbant support put in place;

fill the test tube with liquefied butane;

purge the test tube by a valve situated at the bottom thereof until the butane no longer leaves in liquid phase;

weigh the test tube to determine the weight of adsorbed butane.

As it practically is impossible to determine and to measure each free space in a capillary mass more or less compressed, there is shown in the graph in FIG. 1 (non-underlined numerals on the abscisse) the actual volume of the adsorbant supports as well as the percentages of the volume of the chamber which these actual volumes represent.

The volume of the free space in which it is possible to store the butane being equal to the difference between the total volume of the test tube and the actual volume of the adsorbant support contained in the said test tube, it is possible to see in the same curve the volume of said free space. This is why on the same graph there is shown below the abscissa a scale of underlined numbers giving this volume.

The ordinate shows the volume of adsorbed butane.

Each curve carries the number of the adsorbant support to which it corresponds.

From the assembly of the curves, there is derived Table I following which shows the values of liquefied butane that it is possible to store in 2 cm³, 5 cm³, 7 cm³, and 10 cm³ of actual volume of adsorbant supports having the same apparent volume, to obtain a distribution exclusively in the gaseous phase:

                  TABLE I                                                          ______________________________________                                         Adsorbant                                                                      Support  2 cm.sup.3                                                                               5 cm.sup.3                                                                               7 cm.sup.3                                                                             10 cm.sup.3                               ______________________________________                                         No. 1    9 cm.sup.3                                                                               16 cm.sup.3                                                                              18.5 cm.sup.3                                                                          18 cm.sup.3                               No. 2    9 cm.sup.3                                                                               14 cm.sup.3                                                                              16  cm.sup.3                                                                           17 cm.sup.3                               ______________________________________                                    

It follows, therefore, from the attached drawing as well as from Table I that the compression of the adsorbant support leads in a first phase to an augmentation of the quantity of butane that is was possible to store in a given volume while assuring its distribution exclusively in gaseous phase.

This signifies, that in this first phase, the diminution of apparent volume of a given weight of adsorbant support has been more rapid than the diminution of volume of butane that it was possible to store in this apparent volume to effect a distribution exclusively in the gaseous phase without the need for any intervening special evaporation apparatus.

It is thus noted that for each capillary product tested, there exists an optimum value of the actual volume of the adsorbant support with respect to the total volume of the storage chamber.

Additionally from a multiple number of tests, it is determined that the optimum percentage of actual volume relative to the volume of the storage chamber is, for a polyolefin, about 25%.

Table II following gives for a constant actual volume A of adsorbant support and relative to the results of a first test the quantity of liquefied butane stored when the apparent volume of this adsorbant support is reduced to 40% (second test), 25% (third test) and 10% (fourth test).

                  TABLE II                                                         ______________________________________                                                Test No. 1                                                                             Test No. 2                                                                               Test No. 3                                                                               Test No. 4                                  ______________________________________                                                Apparent volumes of the adsorbant support for                                  a constant actual volume                                                ______________________________________                                                A       40% A     25% A     10% A                                       ______________________________________                                         Adsorbant                                                                      support  1         0.710     0.522   0.200                                     No. 1                                                                          Adsorbant                                                                      support  1         0.622     0.455   0.189                                     No. 2                                                                          ______________________________________                                    

The process of storage according to the invention finds direct application in all cases where a liquefied gas is distributed in an atmosphere whose pressure is less than the pressure of storage. This is the case, for example, for aerosol distributors, for apparatus for the combustion of a combustible gas and notably cigarette lighters. In unexpected fashion, it is found additionally that the reservoirs containing liquefied gas in the presence of an adsorbant support, according to the invention, liberate the gaseous phase under a pressure substantially constant without it being necessary to utilize an expansion means. This is particularly advantageous and economical for gas distributor notably for a combustible gas. 

What is claimed is:
 1. A process of storing a liquefied gas for distribution exclusively in gaseous form into an atmosphere whose pressure is less than that of the storage chamber, the liquefied gas being combustible and being stored in the storage chamber constituted by a feed reservoir of a device having a burner directly connected to an evacuation orifice of the reservoir without interposition of auxiliary gas evaporation apparatus and without auxiliary expansion apparatus, said process comprising disposing in the storage chamber conjointly with the stored liquefied gas, quantity of a capillary adsorbant support having open cells, the minimum value of the actual volume of the support, constituted by the volume remaining after deduction of all interstitial spaces, going from (a) 2% of the volume of the storage chamber for a capillary support having open cells the mean volume of each, once in place, being equal to that of a sphere of a diameter of 40 microns with a mean thickness of the intercellular wall of about 4 microns to (b) 12% of the volume of the storage chamber for a capillary support having open cells in which the mean volume of each cell, once in place, being equal to that of a sphere of a diameter of 200 microns with a mean thickness of the intercellular wall of 30 microns, the amount of liquefied gas disposed in the chamber corresponding to the volume of the support such that all the liquefied gas is adsorbed by the support and only gaseous form of the liquefied gas is discharged upon opening of the evacuation orifice, the said minimum value of the actual volume of the support being of such magnitude to be sufficient to insure the distribution of the liquefied gas exclusively in gaseous form to the burner without auxiliary gas evaporation apparatus and auxiliary expansion apparatus.
 2. A process as claimed in claim 1 wherein the adsorbant support is a polyurethane foam.
 3. A process as claimed in claim 1 wherein the actual volume of the adsorbent support with respect to the total volume of the support is about 25%. 